This invention relates to cooling arrangements in which an expandable bellows is to be prevented from overheating and to certain devices which incorporate cooling arrangements. The need arises to incorporate bellows into high power electronic components, which operate at power levels which can cause a great deal of energy to be dissipated within the bellows itself. A bellows is often incorporated into a high power variable capacitor to enable the vanes of the capacitor to be mounted within an evacuated enclosure, whilst permitting them to be moved as necessary to effect variation of the capacitance. It is possible to pass a fluid coolant over the surface of the bellows to prevent the temperature rising excessively, but it has proved extremely difficult to prevent the occurrence of localised hot spots at which serious overheating of the bellows can occur. It is believed that these difficulties stem from the convoluted configuration of a bellows surface and the present invention seeks to provide an improved cooling arrangement and a variable capacitor incorporating such an arrangement.